Self-lubricating sintered sliding bearingsSELF-LUBRICATING SINTERED
SLIDING BEARINGS
Modern bearing technology in sintered metal: We have the right
solution for you
TM
METALLURGY
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SPECIAL FORMS In addition to standard geometries such as
cylindrical, flanged and spher- ical bearings, developments in pow-
der metallurgy also enable complex geometries for special-purpose
appli- cations.
FIELDS OF USE Typical automotive applications in- clude bearings
for windshield wipers, window mechanisms, seat adjusters, sunroofs
and fan motors. They can also be used in a variety of smaller
electric motors and household actua- tors, in the consumer goods
industry or in general mechanical engineering applications.
MEASUREMENT ENGINEERING • Oil content diagnostic/ soxhlet
extraction
• Testing of sintered density in accordance with DIN EN 2738
• Infrared spectrum for lubricants
SINTERED SLIDING BEARINGS FROM GKN SINTER METALS
OVERVIEW OF MATERIALS Sintered iron and sintered bronze with GKN
Development and design exper- tise for optimum customer
satisfaction
GLOBAL MARKET LEADER Sintered sliding bearings are an indispensable
element of ma- chinery, and GKN Sinter Metals is an expert in their
development and production. Each year, we pro- duce over one
billion high-quality bearings for our customers.
Relevant experience in sintered sliding bearing technology Very
broad selection of available materials and lubricants
Special-purpose equipment compression molds, fur- naces, handling,
sizing, deburring and impregnation Technical support for cust-
omers in the design and appli- cation of sintered bearings
Established development partner
Sintered sliding bearings from GKN Sinter Metals
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THE STRIBECK CURVE The Stribeck curve indicates friction as a
function of linear or rotational speed. The hydro- dynamic range
represents the ideal operating conditions for sintered sliding
bearings.
The viscosity of the lubricant also plays a critical role in defin-
ing the characteristic form of the Stribeck curve and consequent-
ly also the tribological system of the application.
PROPERTIES OF SINTERED SLIDING BEARINGS
• Self-lubricating
• Temperature curve
• We help with the selection of the right materials
IN-LABORATORY SERVICE • Analysis on motors
• Determination of remaining oil
Friction coefficients relative to rota- tional speed
Cylindrical bearing in the gear of a windscreen wiper drive
mechanism
For applications that also func- tion in mixed friction ranges,
additional lubrication with solid lubricants is also
possible.
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SURFACE PROPERTIES The microroughness of the bear- ing surface
enables just the right amount of lubricant to be trans- ferred.
Tests have shown that surfaces that are too smooth or too polished
can diminish the ca- pacity and the life of the bearing. To achieve
the perfect surface properties for the intended func- tion, the
calibration of sintered surfaces offers fascinating op-
portunities. For optimum lubricant stor- age while ensuring that
the oil can circulate through the open pores, GKN determines the
op- timum calibration level for the applications in question.
Finished component
PRODUCTION PROCESS OF SINTERED SLIDING BEARINGS
The bearing sizes start from an interior diameter of 0.8 millime-
ters and can go up to 150 milli- meters.
The calibration ensures that the specified tolerance, especially in
the bore, is adhered to without closing the pores. The final step
is impregnation under vacuum conditions using a suitable
lubricant.
Metal powder
Impregnation
Calibration
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TOLERANCES Our sintered sliding bearings can be manufactured in
accor- dance with the primary DIN, ISO and MPIF standards, but can
also deviate from these to meet your requirements.
Some testing methods used to determine the surface properties of
compact materials cannot be used with PM materials due to their
porosity. The surface roughness of PM components can be described
with better accuracy and in particular better relevance to the
given application using the Abbott curve.
Apparatus to measure cylindrical form
Roughness measuring device
ROUGHNESS OF BEARING SURFACES
Sintered sliding bearing (hydrodynamic)
DU sleeve
Plastic sleeve
DRY BEARINGS WITH SOLID LUBRICANTS Dry lubrication under certain
circumstances can achieve better friction coefficients than plastic
bearings and coated bearings, for instance.
The range of applications of PM bearings
TRIBOLOGICAL SYSTEM
Reduced running sounds, good emergency running properties
ADDITIONAL LUBRICATION: An additional lubricant reserve enables the
service life to be increased considerably. The ef- ficiency is
significantly depen- dent on the chosen reservoir, such as
oil-saturated felt.
SOLID LUBRICANTS: • Graphite • MoS2 • Fe3O4
Friction coefficients of various bearing types
Electric motor with spherical bearings and oil-saturated felt
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FROM PRECISION ENGINEERING TO HEAVY-DUTY INDUSTRIAL APPLICATIONS
Sintered sliding bearings have proven their value superbly for
decades in all engineering dis- ciplines. Their excellent bearing
properties are significantly de- fined by the high level of preci-
sion in their manufacture and the porosity of the sintered
material. Sintered bearings are deployed in almost all fields of
industrial production, from simple guide bearings to high-load
support bearings.
They range from minuscule bearings used in precision engi- neering
to large-scale bearings in heavy-duty industry.
LOAD DIAGRAM With critical requirements such as frequent stopping
& starting, oscillating motion, superior heat discharge or
anti-corrosion properties, we recom- mend the use of sintered
bronze. For highly cost-efficient applications and with more
moderate corrosion resistance requirements, sintered irons can be
used. As the load diagram shows, the use of suitable materials
enables the critical load curves to be moved up to higher
values.
Critical load diagram for sintered bearings
TRIBOLOGICAL SYSTEM The three fundamental factors of a tribological
system:
• Main body (bearing)
• Transmission medium (lubricant)
• Opposing body (shaft)
Only a perfect constellation of these three factors can create a
technically flawless solution.
RANGE OF APPLICATIONS OF SINTERED BEARINGS
ROTATIONAL SPEED (m/s)
• For conventional use
• Speed up to 2 m/s
BRONZE & BRONZE LIGHT* • Radial load up to 5 N/mm2
• Speed up to 3 m/s
• Good emergency running properties
* Lower-cost material mixture while maintaining constant
performance
** under the same environmental conditions (temperature, humidity,
etc.)
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PHYSICAL PROPERTIES
VISCOSITY (FLOW PROPERTIES) Viscosity is the internal friction
(lubricant friction) of a fluid. Vis- cosity is a fundamental
property that describes how thin or thick an oil is. The value is
specified in units of mm²/s at 0 °C and 40 °C (formerly cSt).
VISCOSITY COEFFICIENT These constants describe how dependent the
viscosity is on temperature. It indicates the increase of viscosity
relative to temperature. The lower it is (i.e. the flatter the
viscosity/temper- ature curve), the better the vis-
cosity/temperature properties of the oil.
DENSITY This value remains almost con- stant within a single group
of lubricants. In general, density rises with increasing viscosity.
Density is also no conclusive indication of quality; it is simply a
means of classification, for in- stance.
FLASHPOINT The flashpoint defines the low- est temperature at which
the oil fumes can catch fire as a result of an external ignition
source.
POUR POINT The pour point defines the low- est temperature at which
the lu- bricant still flows.
COLOR The oil color is no indication of its quality.
LUBRICANT TYPES
MINERAL OILS:
These are the most commonly used lubricants, not just because of
their low prices, but also their good lubrication properties. They
are used under bearing temperature conditions ranging from -20 to
+80 °C.
SYNTHETIC OILS:
These purely synthetic products are categorized into chemically
very differ- ent groups. Their advantage lies in their high purity
level – a result of the production process – and their greater
material consistency compared to mineral oils. The use of selective
additives enables the physical properties to be enhanced.
The most important groups are:
Poly-alpha-olefins (synthetic hydrocarbons):
These have a broad practical temperature range of -40 to 120 °C and
for brief periods of up to 150 °C. Their fundamental chemical
structure is similar to that of mineral oils, but they have a
superior viscosity/temperature coefficient and high load ca-
pacity.
Ester oils:
These have a practical temperature range of -50 to 100 °C. They
have ex- cellent wetting properties and are resistant to low
temperatures. This lubri- cant can be aggressive on plastics and
requires compatibility testing.
Silicone oils:
These have a broad practical temperature range of -60 °C to +180
°C. They have a high viscosity coefficient, meaning that it
performs very well in its viscosity to temperature ratio. They are
less resistant to stress then mineral oils. Silicone oils cannot be
mixed with other oils. Disadvantage: Flow properties
Perfluorinated polyether oils: High-temperature lubricant oils for
temperatures from -50 °C to around 200 °C. They exhibit very low
evaporation losses and are suitable for very long service lives at
high temperatures.
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POUR POINT (°C)
150 -50 -50 +100
Perfluorinated polyethers
OTHER PHYSICAL PROPERTIES
EVAPORATION LOSS Evaporation loss is the weight loss of the oil
expressed as a percentage when heated.
PLASTIC COMPATIBILITY When installing sliding bear- ings made of
sintered metal in plastic housings, or when using axial thrust
washers made of plastic, their compatibility with the lubricant
must be tested be- forehand.
Viscosity relative to temperature for different oil types
Overview and properties of lubricants
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BEARING FORMS AND LUBRICANT CONTENT
OIL CONTENT Sintered bearings have a pore volume of between 15 and
30 per cent, and these pores are used as an oil reservoir for the
bear- ing's entire service life. Mineral and synthetic oils are
used for lubrication.
The lubricant reaches the friction area via the pores, with a
system of balance developing over the course of the bearing's
operation.
Weight: 0.520 g Porosity: 20% Oil content: 0.0105 g Service life
10,000 h
Example: PC fan
Example: Timer gear
Weight: 1.450 g Porosity: 25% Oil content: 0.040 g Service life:
30,000 h
FLANGE BEARINGS Differ from cylindrical bearings with their flange
on one side. This serves as a restraint during installation, and in
certain cases, also serves as a larg- er support when placed under
axial loads. This form of bearing also needs to be pushed in using
a mandrel.
SPHERICAL BEARINGS Guarantees autonomous re-alignment of the
bearing bore. The bore diameter remains unchanged when installing
the spherical bearing. However, the installation is somewhat more
compli- cated.
SPHERICAL BEARING WITH EXTENSION The main purpose of the extension
is to compensate for any in-between spaces.
CYLINDRICAL BEARINGS This most cost-effective form of bear- ing is
primarily pushed into a pre-pro- cessed bearing bore using a
mandrel.
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18) Shaft roughness
...................................................µm
20) Misc. details
...........................................................................................................................................
6) Mode of operation uninterrupted .................. interrupted
.................................................
7) Required service life
................................................ h 8) Speed
.................................................. rpm
9) Lubricant reservoir yes no ............................... 10)
Oil type ....................................................
11) Total bearing load (radial)
...................................... N 12) Specific
.......................................... N/mm2
13) Bearing load (axial)
................................................ N
14) Bearing operating temperature ............................. °C
15) Ambient temperature ............................ °C
© Copyright by GKN Sinter Metals 2020
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